Episode(s): "I Have No Son" (Season 2, Episode 1) and "The Lounge Singer" (Season 2, Episode 3)
Air date: 9/25/1994 & 10/9/1994
In the former episode Mr. Bighead's son, Ralph Bighead, is introduced as a cartoonist, which leads to his estrangement from his family. His father wanted him to be a corporate man. In the latter, there's Filbert, whose dreams of being a lounge singer lead to him hitting the big time.
Both of these episodes are important because they showcase the importance of doing what you want to do, instead of doing what you "should" do. "I Have No Son" was actually inspired by issues affecting show creator Joe Murray, as well as other directors and writers. Regardless of how cliche it is, do what makes you happy. Even if that means you want to be a lounge singer.